1. Field of the Invention
The present invention relates to a plasma display panel (hereinafter referred to also as xe2x80x9cPDPxe2x80x9d), and more particularly, it relates to a technique of improving display quality such as luminance of an alternating current PDP (hereinafter referred to also as xe2x80x9cAC-PDPxe2x80x9d).
2. Description of the Background Art
FIG. 30 is an exploded perspective view showing a conventional AC-PDP 101P. As shown in FIG. 30, the AC-PDP 101P is roughly classified into a front panel 101FP and a rear panel 101RP.
In the front panel 101FP, a transparent dielectric thin film layer 55P containing no alkaline metal such as sodium (Na) is formed on a main surface of a glass substrate 51 made of soda-lime glass, for example. The dielectric thin film layer 55P is formed through a thin film forming process such as CVD method, for example. In general, the insulation resistance of soda-lime glass or the like is reduced when the temperature is increased, and hence inconvenience may result in operations of the AC-PDP 101P due to heat generated in operation. The dielectric thin film layer 55P is provided for ensuring insulation of sustain electrodes 10P and 20P described later.
Strip-shaped sustain electrodes 10P and 20P forming sustain electrode pairs 30P are formed in parallel with each other through prescribed gaps (discharge gaps) g on the surface of the dielectric thin film layer 55P opposite to glass substrate 51. A plurality of such sustain electrodes 10P and 20P are alternately formed in the form of stripes. The sustain electrodes 10P and 20P consist of transparent electrodes 11P and 21P formed on the aforementioned surface of the dielectric thin film layer 55P and metal electrodes (referred to also as xe2x80x9cbus electrodesxe2x80x9d) 12P and 22P formed on surfaces of the transparent electrodes 11P and 21P opposite to the glass substrate 51.
As described later, display emission is taken out from the side of the glass substrate 51. Therefore, the transparent electrodes 11P and 21P are employed for increasing discharge areas, i.e., electrode areas while not screening visible light converted/generated in fluorescent materials 75R, 75G and 75B described later.
The transparent electrodes 11P and 21P have high electrode resistance, and hence these transparent electrodes 11P and 21P are combined with the metal electrodes 12P and 22P thereby reducing the resistance of the sustain electrodes 10P and 20P.
The transparent electrodes 11P and 21P are prepared from ITO or SnO2, for example, while the metal electrodes 12P and 22P are formed by thick films of Ag or the like or thin films having a three-layer structure of Cr/Cu/Cr or a two-layer structure of Al/Cr, for example.
A black pattern (hereinafter referred to also as xe2x80x9cin-electrode black layerxe2x80x9d) of the same size or shape as the metal electrodes 12P and 22P is formed between the metal electrodes 12P and 22P and the transparent electrodes 11P and 21P, although FIG. 30 omits illustration of such an in-electrode black layer in order to avoid complication. The in-electrode black layer, which must electrically connect the metal electrodes 12P and 22P with the transparent electrodes 11P and 21P, is made of a conductive material.
On the aforementioned surface of the dielectric thin film layer 55P, a stripe-shaped black pattern (the so-called black stripe pattern) 76P is formed between adjacent sustain electrode pairs 30P in parallel with the sustain electrodes 10P and 20P. In order to avoid complication of illustration, FIG. 30 shows the black stripe pattern 76P only in the fragmented portion. Dissimilarly to the aforementioned in-electrode black layer, the black stripe pattern 76P is made of an insulating material. If made of a conductive material, the black stripe pattern 76P disadvantageously serves as an electrode to readily induce discharge (false discharge) between the same and the sustain electrode pairs 30P.
According to the in-electrode black layer and the black stripe pattern 76P, reflection of external light can be more reduced as viewed from the side of the front panel 101FP forming the display surface of the AC-PDP 101P, thereby consequently improving the contrast. The reason for this is as follows: Under light environment, the contrast, decided by the ratio of (i) reflection intensity of external light when the PDP emits no light to (ii) luminous intensity when the PDP emits light, is increased as the reflection intensity of external light is reduced under constant luminous intensity. Therefore, reflection of external light is preferably minimized, as enabled by the in-electrode black layer and the black stripe pattern 76P.
At this time, light generated in a discharge space, defined by the front panel 101FP and the rear panel 101RP, is screened by the opaque metal electrodes 12P and 22P arranged closer to the discharge space than the in-electrode black layer when taken out from the AC-PDP 10P. In addition, the in-electrode black layer is identical in size to the metal electrodes 12P and 22P as described above. In consideration of these points, the numerical aperture, i.e., luminous intensity is not reduced due to provision of the in-electrode black layer.
The black stripe pattern 76P is provided between adjacent discharge cells in the direction perpendicular to the sustain electrodes 10P and 20P. In other words, the black stripe pattern 76P is provided on a region irrelevant to display emission, and hence reduction of luminance is small despite provision of the black stripe pattern 76P.
A transparent dielectric layer 52 is formed to cover the dielectric thin film layer 55P and the sustain electrodes 10P and 20P. The dielectric layer 52 has a role of isolating the sustain electrodes 10P and 20P from each other while isolating the sustain electrodes 10P and 20P from the discharge space defined by the front panel 101FP and the rear panel 101RP or discharge formed in the discharge space. A protective film 53 of MgO, for example, is formed on the dielectric layer 52. The protective film 53 has a role of protecting the dielectric layer 52 from the discharge formed in the discharge space while serving as a secondary-electron emission film for reducing a (discharge) firing voltage.
In the rear panel 101RP, on the other hand, a plurality of strip-shaped write electrodes 72 are formed in the form of stripes on a main surface of a glass substrate 71. A dielectric layer 73 is formed on the aforementioned main surface of the glass substrate 71 to cover the write electrodes 72. Further, barrier ribs (also simply referred to as xe2x80x9cribsxe2x80x9d) 74 are formed on regions corresponding to those between adjacent two write electrodes 72 on a surface of the dielectric layer 73 opposite to the glass substrate 71. End portions or top portions of the barrier ribs 74 separated from the glass substrate 71 are blackened by a black material, for example. Such black portions 74T, referred to as black stripe or black matrix, act to improve the contrast of display emission. Fluorescent materials or fluorescent layers 75R, 75G and 75B for emitting light of red (R), green (G) and blue (B) are arranged on inner surfaces of U-shaped trenches defined by adjacent two barrier ribs 74 and the dielectric layer 73 respectively. There is also a rear panel having no dielectric layer 73.
The front panel 101FP and the rear panel 101RP are so arranged that the aforementioned main surfaces of the glass substrates 51 and 71 face each other in such a direction that the sustain electrodes 10P and 20P and the write electrodes 72 three-dimensionally intersect with each other, while the peripheries thereof are airtightly sealed. The striped discharge space defined between the front panel 101FP and the rear panel 101RP and divided by the fluorescent layers 75R, 75G and 75B (may be grasped as divided by the barrier ribs 74) is filled with discharge gas containing xenon (Xe), neon (Ne) or the like. Each of the three-dimensional intersections between the sustain electrode pairs 30P or the discharge gaps g and the write electrodes 72 define a single discharge cell or a single light emitting cell.
The outline of the principle of a display operation on the AC-PDP 101P is as follows: AC pulses are applied to the sustain electrode pairs 30P for discharging the discharge gas through the discharge gaps g and converting ultraviolet rays generated by this discharge to visible light by the fluorescent layers 75R, 75G and 75B. This visible light is taken out from the side of the glass substrate 51 for display emission.
At this time, emission/non-emission of each light emitting cell is controlled as follows: First, discharge (write discharge) is previously formed between the write electrode 72 and the sustain electrode 10P or 20P in the desired light emitting cell(s) for display emission. Wall charges are formed on a portion of the protective film 53 corresponding to the desired light emitting cell(s) due to this discharge. Thereafter a prescribed voltage (sustain voltage) is applied to the sustain electrode pair 30P for causing discharge (sustain discharge) only in the light emitting cell(s) formed with the wall charges. In other words, a sustain voltage of a value causing discharge in the light emitting cell(s) having wall charges while causing no discharge in light emitting cells having no wall charges is applied. Thus, a desired light emitting cell can be selected for emitting light. The sustain voltage can be simultaneously applied all over the AC-PDP 101P.
Transparent conductive thin films of ITO, SnO2 or the like can be applied as the transparent electrodes 11P and 21P, as described above. Frequently employed ITO and SnO2 are now compared with each other. While ITO is superior to SnO2 in conductivity, transparency and patterning workability, but the former is inferior in stability of chemical resistance and heat resistance to the latter. Further, it is difficult for ITO, generally subjected to film formation by physical vapor deposition method such as vacuum deposition, sputtering or ion plating, to satisfy formation over a wide area and mass production.
On the other hand, SnO2 has characteristics opposite to those of ITO. In other words, SnO2 is superior in stability of chemical resistance and heat resistance to ITO. Further, SnO2, generally subjected to film formation by chemical vapor deposition (CVD) method, readily satisfies formation over a wide area and mass production. However, SnO2 is inferior in conductivity and transparency to ITO, and it is difficult for SnO2 to attain patterning in higher precision or higher definition to ITO due to the aforementioned superior stability of chemical resistance. Thus, each of ITO and SnO2 has its merits and demerits, and it is hard to tell which is the best.
As hereinabove described, the sustain electrodes 10P and 20P have the two-layer structure of the transparent electrodes 11P and 21P and the metal electrodes 12P and 22P, and hence the metal electrodes 12P and 22P must be formed in correct alignment. Thus, inconvenience in such alignment results in reduction of the yield.
Japanese Patent Application Laid-Open No. 10-149774 (1998) discloses an AC-PDP capable of rendering material selection of transparent electrodes and alignment unnecessary. FIG. 31 is a typical top plan view showing such an AC-PDP 101P as viewed from the side of a front panel, with extraction and illustration of only a sustain electrode pair 130P and barrier ribs 74.
As shown in FIG. 31, the sustain electrode pair 130P consist of sustain electrodes 110P and 120P, which are formed by four strip-shaped thin electrodes or thin-line electrodes 112aP to 112dP and four strip-shaped thin electrodes or thin-line electrodes 122aP to 122dP respectively. The thin-line electrodes 112aP to 112dP and 122aP to 122dP are arranged in parallel with each other and perpendicularly to the barrier ribs 74. A clearance between the adjacent thin-line electrodes 112aP and 122aP defines a discharge gap g, while the remaining thin-line electrodes separate from the discharge gap g in order of the thin-line electrodes 112bP and 122bPxe2x86x92the thin-line electrodes 112cP and 122cPxe2x86x92the thin-line electrodes 112dP and 122dP. The thin-line electrodes 112aP to 122dP and 112aP to 122dP are formed not by transparent conductive thin films but by metal thin films having lower resistance than transparent conductive films. Thus, the sustain electrodes 110P and 120P are formed by the thin-line electrodes 112aP to 112dP and 122aP to 122dP corresponding to the bus electrodes 12P and 22P respectively.
In the AC-PDP 102P visible light is taken out from clearances between the thin-line electrodes 112aP to 112dP and 122aP to 122dP respectively. The sustain electrodes 110P and 120P, formed by the four thin-line electrodes 112aP to 112dP and the four thin-line electrodes 122aP to 122dP as described above, can ensure electrode areas or discharge areas to some extent. Therefore, luminance necessary for screen display can be attained to a certain extent without providing the transparent electrodes 11P and 21P provided on the aforementioned AC-PDP 101P.
According to the sustain electrodes 110P and 120P, manufacturing is easier and manufacturing steps are simplified since it is not necessary to form the transparent electrodes 11P and 21P of the AC-PDP 101P. Further, no equipment is necessary for forming transparent electrodes. Consequently, the manufacturing cost can be reduced.
When observing luminous intensity in a single light emitting cell from the side of the front panel in each of the AC-PDPs 101P and 102P, its distribution has the following general tendencies. This is described with reference to FIG. 32. FIG. 32 shows a typical top plan view of the AC-PDP 101P, extracting and illustrating only the transparent electrode 11P and the barrier ribs 74, luminance distribution along the longitudinal direction of the transparent electrodes 11P and 21P, and luminance distribution along the longitudinal direction of the barrier ribs 74.
First, there is such a tendency that the luminance is increased as approaching side surfaces of the barrier ribs 74, as shown in FIG. 32. This is conceivably because portions of the fluorescent layers 75R, 75G and 75B located on the aforementioned side surfaces (particularly portions close to the sustain electrodes 10P and 20P) are irradiated with a larger quantity of ultraviolet rays since the same are closer to the discharge gaps g than portions located on the dielectric layer 73 (see FIG. 30). The aforementioned portions of the fluorescent layers 75R, 75G and 75B have smaller loss when taking out visible light from the AC-PDP 101P since the same are closer to the glass substrate 51. Further, there is such a tendency that the luminance is increased as approaching the discharge gaps g, as shown in FIG. 32. This is conceivably because the discharge strength, i.e., the quantity of ultraviolet rays is at the maximum around the discharge gaps g and reduced as separated from the discharge gaps g. According to these, it is understood that the luminance is increased as approaching both the discharge gaps g and the barrier ribs 74.
In consideration of the luminance distribution shown in FIG. 32, it is hard to say that the quantity of visible light taken out from the AC-PDP 102P, i.e., the luminance of the AC-PDP 102P is optimized or maximized. This is because the thin-line electrodes 112aP to 112dP and 122aP to 122dP, (three-dimensionally) intersecting with the barrier ribs 74, screen high-luminance emission around the discharge gaps g and the barrier ribs 74, as understood when observing FIG. 31.
When increasing the distances between the adjacent ones of the thin-line electrodes 112aP to 112dP and 122aP to 122dP, it is possible to increase the numerical aperture and improve the quantity of the taken-out light, i.e., the luminance. When increasing the aforementioned distances, however, the thin-line electrodes 112aP to 112dP and 122aP to 122dP serve as independent electrodes respectively and hence it is difficult to form electric fields formed by the sustain electrodes 110P and 120P, to be integrally formed by the four thin-line electrodes 112aP to 112dP and the four thin-line electrodes 122aP to 122dP.
When changing the voltage applied to the sustain electrodes 110P and 120P, therefore, there appears such a phenomenon that discharge spreads in a plurality of stages of steps as discharge between the thin-line electrodes 112aP and 122aPxe2x86x92discharge between the thin-line electrodes 112bP and 122bPxe2x86x92. . . , Such a phenomenon may unstabilize discharge depending on the set value of the voltage applied to the sustain electrodes 110P and 120P. In other words, this phenomenon may cause such a situation that discharge cells forming discharge between the thin-line electrodes 112bP and 122bP and between the thin-line electrodes 112cP and 122cP are intermixed, for example. Such instability of discharge, observed as luminance unevenness, reduces discharge quality of the AC-PDP. In order to eliminate such instability of discharge, the set voltage must be extremely correctly controlled.
While the width of the thin-line electrodes 112aP to 112dP and 122aP to 122dP themselves may be reduced in order to increase the numerical aperture, patterning is disadvantageously rendered difficult as the width is reduced.
Although the in-electrode black layer and the black stripe pattern 76P of the AC-PDP 101P attain similar functions/effects of improving the contrast, the in-electrode black layer made of a conductive material and the black stripe pattern 76P made of an insulating material. Therefore, the in-electrode black layer and the black stripe pattern 76P must disadvantageously be formed through different steps.
A substrate for a plasma display panel according to a first aspect of the present invention comprises a transparent substrate and at least one pair of electrodes arranged on the side of one main surface of the transparent substrate each having a base portion and a projecting portion which is coupled with the base portion and projects from the base portion along the main surface, while the electrodes are formed only by an opaque conductive material and the projecting portions of the electrodes project toward each other to form a discharge gap between the projecting portions.
According to the first aspect, the respective projecting portions project from the respective base portions toward each other. In other words, the base portions are present on positions separate from the discharge gap. When applying the substrate for a plasma display panel to a plasma display panel, therefore, the quantity of visible light screened by the base portions is smaller as compared with a structure having base portions around a discharge gap. Therefore, a larger quantity of visible light can be taken out. Thus, the substrate for a plasma display panel can provide a plasma display panel having high luminance.
According to a second aspect of the present invention, each of the projecting portions includes a first portion coupled with the base portion to extend in a projecting direction of the projecting portion and a second portion coupled with an end of the first portion separated from the base portion, and the second portions of the projecting portions face each other to form the discharge gap.
According to the second aspect, the quantity of visible light screened by the projecting portion can be reduced by setting a T shape, for example, by the first and second portions. Thus, a plasma display panel of high luminance can be provided.
Further, the second portion forming the discharge gap is coupled with the first portion, whereby discharge caused in the discharge gap can be expanded toward the base portion through (not a plurality of stages of steps but) a single step also when an applied voltage is increased. Therefore, a plasma display panel having no luminance unevenness resulting from expansion of discharge through a plurality of stages of steps can be provided. In addition, a set margin for the applied voltage can be more widened as compared with the aforementioned conventional plasma display panel.
According to a third aspect of the present invention, the projecting portion has a shape including at least one of an O shape, an L shape and a U shape.
According to the third aspect, the projecting portion includes at least one of an O shape, an L shape and a U shape, whereby it is possible to provide a plasma display panel capable of taking out a larger quantity of visible light through an opening or a clearance defined by such a shape. In this case, the projecting portion can be reliably patterned by defining a U-shaped projecting portion by two first portions and the second portion.
According to a fourth aspect of the present invention, the projecting portion has a discharge-gap-forming-portion facing the discharge gap to form the discharge gap, and the discharge-gap-forming-portion is shorter than a remaining portion of the projecting portion other than the discharge-gap-forming-portion along a direction perpendicular to a projecting direction of the projecting portion.
According to the fourth aspect, high-intensity emission around the discharge gap can be taken out in a larger quantity, whereby luminance and luminous efficiency can be improved.
According to a fifth aspect of the present invention, the at least one pair of electrodes includes a plurality of pairs of electrodes arranged at a prescribed pitch in a projecting direction of the projecting portion, and satisfies the following relation:
xe2x80x83b less than (pxe2x88x92gxe2x88x92115)/2.42
assuming that p (xcexcm) represents the prescribed pitch while b (xcexcm) and g (xcexcm) represent the lengths of the projecting portion and the discharge gap in a projecting direction respectively.
According to the fifth aspect, it is possible to provide a plasma display panel capable of suppressing false discharge between electrode pairs adjacent to each other in the projecting direction of the projecting portion.
According to a sixth aspect of the present invention, the at least one pair of electrodes includes a plurality of pairs of electrodes arranged in a projecting direction of the projecting portion, and the substrate for a plasma display panel further comprises a black insulating layer arranged between the pairs of electrodes and the transparent substrate and between adjacent ones of the pairs of electrodes.
According to the sixth aspect, contrast can be improved by the black insulating layer. When preparing respective portions located between the electrode pairs and the transparent substrate and between adjacent ones of the electrode pairs from the same material, both portions can be simultaneously formed.
According to a seventh aspect of the present invention, the at least one pair of electrodes includes a plurality of pairs of electrodes, and electrode areas of all projecting portions are not identical to each other.
According to the seventh aspect, the discharge current quantity can be set for each projecting portion (or each discharge cell). Therefore, it is possible to provide a plasma display panel improved in luminance and/or having a desired white color temperature by setting the discharge current quantity, i.e., setting the quantity of ultraviolet rays.
According to an eighth aspect of the present invention, the substrate for a plasma display panel further comprises a dielectric layer covering the projecting portions, and the electrode area of each projecting portion is set on the basis of thickness of a portion of the dielectric layer covering each projecting portion.
According to the eighth aspect, it is possible to provide, when the dielectric layer has thickness distribution, a plasma display improved prevented from luminance unevenness with respect to this distribution.
According to a ninth aspect of the present invention, the substrate for a plasma display panel further comprises a secondary-electron emission film over the projecting portions, and the electrode area of each projecting portion is set on the basis of secondary-electron emission efficiency of a portion of the secondary-electron emission film corresponding to each projecting portion.
According to the ninth aspect, it is possible to provide, when secondary-electron emission efficiency of the secondary-electron emission film has distribution, a plasma display panel prevented from luminance unevenness corresponding to the distribution.
According to a tenth aspect of the present invention, the substrate for a plasma display panel further comprises an underlayer arranged between the transparent substrate and the electrodes in contact with the electrodes, formed by a transparent dielectric substance formed at a temperature below the softening point of the transparent substrate, and the electrodes are formed by applying and sintering a paste material of the opaque conductive material.
According to the tenth aspect, the underlayer consists of a dielectric substance formed at a temperature below the softening point of the transparent substrate and the electrodes are formed by applying and sintering a paste material of the opaque conductive material. Therefore, the so-called edge curls can be remarkably reduced by setting the sintering temperature for the paste material of the aforementioned opaque conductive material to a level capable of softening the underlayer. Further, the transparent substrate is not thermally deformed at this time. Thus, it is possible to provide a stably operating plasma display panel with no insulative inconvenience resulting from edge curls of the dielectric layer covering the projecting portion.
A plasma display panel according to an eleventh aspect of the present invention comprises a first substrate including the substrate for a plasma display panel according to any one of the first to tenth aspects, a second substrate, including a strip-shaped counter electrode, arranged to face the first substrate, a barrier rib arranged between the first and second substrates to extend along the counter electrode, and a fluorescent layer arranged on a side surface of the barrier rib, while the projecting portion and the barrier rib do not overlap with each other as viewed from the side of the first substrate.
According to the eleventh aspect, the projecting portion and the barrier rib do not overlap with each other as viewed from the side of the first substrate, so that the projecting portion does not screen visible light emitted from the fluorescent layer on the side surface of the barrier rib. Therefore, high luminance can be attained by taking out a larger quantity of visible light.
According to a twelfth aspect of the present invention, the barrier rib is separated from a portion of the projecting portion extending in a projecting direction of the projecting portion by at least 70 xcexcm as viewed from the side of the first substrate.
According to the twelfth aspect, the aforementioned effect of the eleventh aspect can be more reliably and more remarkably attained.
A plasma display panel according to a thirteenth aspect of the present invention comprises a first substrate including the substrate for a plasma display panel according to the fourth aspect, a second substrate, including plurality of strip-shaped counter electrodes, arranged to face the first substrate such that each electrode has a plurality of projecting portions, and the plasma display panel further comprises a plurality of barrier ribs, extending between the first and second substrates along the counter electrodes, arranged alternately with the counter electrodes not to overlap with the projecting portions as viewed from the side of the first substrate, and a plurality of fluorescent layers arranged on facing side surfaces of adjacent ones of barrier ribs for emitting prescribed luminescent colors defined in units of spaces partitioned by the first and second substrates and the barrier ribs, while an electrode area of each projecting portion is set for every prescribed luminescent color of the fluorescent layer in the space where each projecting portion faces.
According to the thirteenth aspect, difference in luminous intensity among emitted luminescent colors can be corrected when applying the same quantity of ultraviolet rays. Thus, a desired white color temperature can be obtained.
A first object of the present invention is to provide a plasma display panel capable of attaining high-intensity emission while comprising electrodes of an opaque conductive material such as a metal and a substrate for a plasma display panel capable of implementing such a plasma display panel.
A second object of the present invention is to provide a plasma display panel suppressed in luminance unevenness etc. to exhibit high display quality and a substrate for a plasma display panel capable of implementing such a plasma display panel along with implementation of the first object.
A third object of the present invention is to provide a substrate for a plasma display panel having reliably pattern-formable electrodes.
A fourth object of the present invention is to provide a plasma display panel and a substrate for a plasma display panel capable of suppressing false discharge between adjacent electrode pairs.
A fifth object of the present invention is to provide a plasma display panel and a substrate for a plasma display panel capable of improving contrast.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.